Picture quality of printed result (printed matter) required for printer becomes high year by year, and realization of high resolution and realization of multi-valued data are advanced in accordance therewith.
On the other hand, correspondingly thereto, print data becomes vast more and more. For example, data quantity of A4 full size 600 dpi CMYK (cyan, magenta, yellow, black) respective pixel 8 bit becomes equal to as far as about 140 MB. Under such circumstances, it takes much time in data transfer. In view of the above, compression is implemented to such data, or 8 bits are changed into 4 bits or 3 bits to thereby reduce data quantity.
However, even if data quantity is halved by compression and is further changed into 3 bits so that it becomes equal to ⅜, there still exists data quantity of about 26 MB. As a result, it took much time in data transfer.
In view of the above, when respective pixels are caused to be changed into 1 bit so that data quantity is further halved by compression, data quantity is held down to about 9 MB. Accordingly, it is possible to shorten data transfer time down to satisfactory degree. However, since respective pixels are represented by binary number, it becomes difficult to obtain printed matter of high picture quality.